Performance Study On The Impact Of Heat And Mass Recycling Of Biogas Slurry In Thermostatic Biogas Production System

Most of the biogas plants in china come across serious problems such as too much heat consumption, no cheap heat resources and so on. All these problems lead to biogas plants cannot operate stably in cold seasons for stacking of heat. For the purpose of solving these problems, this paper studies how to collect heat from biogas plant itself, and recycles heat from slurry discharged by the Anaerobic fermentation tower, and makes a summery for the problems the biogas plant encountered in Huazhuang cow farm of Lanzhou, and establishes a thermostatic biogas producti on system and dose some improvement for the process according to the problems.This paper gives a detailed energy-flow analysis on the heat load in different months of the digester, the result shows that the heat load of the digestion accounts for 7.1%-8.3% in the whole, the rest is the heat energy loss of methane liquid which accounts 91.7%-92.9% in the whole. The heat energy loss of the digester ef fluent is the most important cause for low temperature of methane biochemical reaction in cold areas by. Thanks to the plant waste heat recovery system,whose efficiency is only 35 percent,the biogas plant can keep operating steadily from May to September in a year. In other months of the year, it cannot be in steady operation because of the poor recovery of heat, and it is in line with the analysis.We makes a transformation for the fermentation system, such as add ing a solid-liquid separating facility, adding a new heat-transferring coil in acidification pool instead of those old heat-transferring coil in digestion tank. Dose some simulation research for the biogas slurry heat recovery pool by FLUENT, in which 22.5m3 effluent at 35℃and 25.3m3 fermentation raw material at 0 ℃ changes heat. 22 hours later, the temperature of fermentation raw material rises 16.24℃, and the heat recovery efficiency of the heat recovery pool is 52.2%; the simulation shows that the Upper and lower temperature difference is big in both side of the slurry heat recovery pool: the lower liquid is colder than the upper. So we make a optimum proposal utilizing this character: pull out 1meter high effluent from the slurry heat recovery pool 14 hours later since it begins exchanging heat. And then, after 8 hours, the temperature of fermentation raw material rises 18.31 ℃ in total, the heat recovery efficiency of the heat recovery pool rises to 58.8%, which is 6.6 percent higher than before.We also reflux 30% biogas slurry into hydrolysis pool at the same time. on account of little heat loss during that process, we believe that all of the energy in 9.7m3 biogas slurry is recycled. Heat recycled from heat recovering pool and mass recycle accounts for 55.9-60.7% of total heat load.Design a biogas slurry heat recovery pool to recycle the heat from 70% of effluent and reflux 30% biogas slurry into hydrolysis pool at the same time, with heat recycled by the plant, the fermentation system can be in steady operation all the year round. Use the very cold days to verify the heat supply whether can keep the fermentation temperature at 35℃, the result is that it can.